The term meshed networks refers to telecommunication networks without node ranking in which every node is connected to at least two further nodes. A fully meshed network is one in which every node is connected directly to every other node in the network. In a meshed network configuration with routing of telecommunication calls, in the event of so-called trunk group bottlenecks there is the danger of loop formation over several network nodes. If the trunk group bottleneck that led to the loop formation is not cleared, then the telecommunication call runs through the loop until all the paths are occupied.
A process for searching for an alternative path in a communication network is already known from the published European Patent Application having the application number 90125088.6. In the known process, first of all the entire network is checked for the failure of one or more nodes and/or the failure of one or more connection paths between two nodes. Following this, the nodes affected by the failures detected must be identified in every path. After that, a message called a "restoration message" which comprises an identification number of the transmitting node and identification numbers of the nodes affected by the failures must be formed. It must also be checked whether one of the aforesaid nodes is the terminal node of an alternative path. Finally, an alternative path through the communication network is determined. Overall, the known process requires a multiplicity of process steps, with the result that there is a considerable load on the controllers involved in the process.
A process termed "telecommunications network route selection" is already known from the published European Patent Application having the application number 90311577.2. A path from a message source to a message destination is selected here on the basis, inter alia, of so-called "busy/idle status information" which must be created and managed over the whole network. In conjunction therewith, in addition a so-called "source destination restriction map" is formed in network nodes in each case. For connections from specific source nodes to a further network node, such a table specifies which of the connection routes going out from this network node are permitted. However, network loops are not precluded here: it is possible for a connection route (e.g. "20") via which the call has already been routed (FIG. 1: 2-11-3-20-1-20 . . . ) to be specified as permitted for a connection from one source node (e.g. source "2") to the further node (e.g. "1").
Processes for establishing telecommunication calls are also already known from German Patent Specification DE 3,626,870 as well as from Laid-Open Publications 1,512,858 and 1,487,989, in which it is provided to some extent that information indicating the originating exchange is inserted into the signaling information. However, this information does not serve to prevent the formation of loops in the known processes. In the process known from German Patent Specification DE 3,626,870, a digital telecommunication network is divided into so-called routing cells comprising a plurality of signaling points in each case. Within a routing cell, of the possible signaling routes, only specific signaling routes between the signaling points are progressively released for selection in the direction of the destination, whereby the circling of signaling messages within a routing cell is avoided. In the process known from German Laid-Open Publication 1,512,858, calls are routed over a relay station designed as a satellite, a free speech path in the forward direction being selected, and a busy signal with an identification signal that identifies the selected speech path and the originating exchange being transmitted to the destination exchange. In the process known from German Laid-Open Publication 1,487,989, additional information relating to the suitability of the path proposed and/or traveled is provided. Furthermore, this process also provides for the formation of information identifying the number of connection elements traveled, checking means being provided in transit exchanges to check this information, and further path searching being terminated once a predetermined maximum number of connection elements traveled on the respective path has been reached.
A communication system ("HICOM 300") that can form a network node in a meshed network is already known from the product publications of Siemens "HICOM 300 System Product Data", Ordering No. A19100-K3161-430-X-7600, pages 55/56, and "Private Kommunikationssysteme, HICOM schafft Verbindungen" [Private communication systems, HICOM makes connections], Ordering No. A19100-K3160-A302, page "HICOM 300 Networking". In the above systems, in the case of telecommunication calls to be established via transit nodes, a check may be provided in transit nodes as to whether a telecommunication call to the destination node is permitted on the basis of a node number identifying the destination node. With such establishment of telecommunication calls, however, there is the danger of network loops forming.